Test contact mechanism

ABSTRACT

The present invention provides test contact systems and associated integrated circuit device testing systems, and integrated circuit device testing methods that reduce the number of integrated circuit devices that are lost through handler mishap. The invention provides a test contact system in which a contacting force, or a substantial portion thereof, is exert against the substrate of a device under test, rather than exerting the entire force against the die. The invention also provides a system for adjusting the distribution of the contacting force between the substrate and the die. This mechanism allow the force against the die to be kept within a range that provides good thermal contact between the die and the test contact mechanism without damaging the die. The balance of the contacting force can be transmitted to the substrate of the device under test through a resilient member, thereby further reducing the risk of damage to the device under test. The invention further provides a vacuum seal comprising a foam type material to which devices under test do not stick, which substantially eliminates handler jambs resulting from devices under test sticking to the vacuum seal. The test contact systems of the invention, and associated testing systems and methods, significantly reduce the number of integrated circuit devices damaged during testing.

TECHNICAL FIELD

The present invention relates to semiconductor testing and testingdevices. In particular, the present invention relates to a system forestablishing contact between a device under test and a test socket.

BACKGROUND OF THE INVENTION

During and after manufacture, integrated circuit devices are subject toexhaustive testing. After an integrated circuit device has beenpackaged, its contacts are coupled to the channels of an integratedcircuit device tester. The tester applies a series of excitations to thedevice and analyzes the device's responses. On the basis of the testresults, the device can be graded and sorted.

Testing is desirably carried out rapidly, accurately, and in highvolume. For these purposes, automated testing equipment has beendeveloped. A typical testing system includes a device tester and adevice handler. The device handler has a test contact system that picksup a device under test, using suction applied through a silicone vacuumseal, and places the device under test into a socket of the devicetester. The test contact system applies a force against the device undertest to establish and maintain electrical contact between the deviceunder test and the test socket.

Where the device under test includes a die mounted on a substrate, thetest contact system typically applies the contacting force against thedie, which is at the center of the substrate. Particularly where the dieis un-encased, as is often the case when the device under test is of theflip chip type, the die or the substrate sometimes cracks, resulting ina loss of the device under test. Devices under test can also be lostwhen a device under test sticks to the vacuum seal resulting in ahandler jam.

There is an unsatisfied need for a device testing system that reducesthe number of devices lost through handler mishaps.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Its sole purpose is to present some conceptsof the invention in a simplified form as a prelude to the more detaileddescription that is presented later.

The present invention provides test contact systems and associatedintegrated circuit device testing systems, and integrated circuit devicetesting methods that reduce the number of integrated circuit devicesthat are lost through handler mishap. The invention provides a testcontact system in which a contacting force, or a substantial portionthereof, is exert against the substrate of a device under test, ratherthan exerting the entire force against the die. The invention alsoprovides a system for adjusting the distribution of the contacting forcebetween the substrate and the die. This mechanism allow the forceagainst the die to be kept within a range that provides good thermalcontact between the die and the test contact mechanism without damagingthe die. The balance of the contacting force can be transmitted to thesubstrate of the device under test through a resilient member, therebyfurther reducing the risk of damage to the device under test. Theinvention further provides a vacuum seal comprising a foam type materialto which devices under test do not stick, which substantially eliminateshandler jambs resulting from devices under test sticking to the vacuumseal. The test contact systems of the invention, and associated testingsystems and methods, significantly reduce the number of integratedcircuit devices damaged during testing.

One aspect of the invention provides a test contact system for exertinga contacting force against an integrated circuit device that comprisesan un-encased die attached to a substrate, comprising a body and acontact plate supported by the body, wherein the contact plate exerts atleast a substantial portion of the contacting force against thesubstrate of the integrated circuit device.

Another aspect of the invention provides a test contact systemcomprising a body, a resilient member, and a contact plate, wherein thebody exerts a repelling force against the contact plate through theresilient member.

A further aspect of the invention provides a test contact systemcomprising a body and a vacuum seal attached to the body for holding adevice under test to the body, wherein the vacuum seal comprises a foamtype material.

A further aspect of the invention provides a test contact systemcomprising means for exerting a contacting force against an integratedcircuit device, wherein the integrated circuit device comprises anun-encased die attached to a substrate and at least a substantialportion of the contacting force is exerted against the substrate of theintegrated circuit device.

A further aspect of the invention provides a method of testing anintegrated circuit device comprising , while testing the integratedcircuit device, exerting a contacting force to hold the device undertest in contact with a socket of a device tester, wherein at least asubstantial portion of the contacting force is exerted against asubstrate of the device under test.

The invention extends to features hereinafter fully described andfeatures particularly pointed out in the claims. The following detaileddescription and the annexed drawings set forth in detail certainillustrative examples of the invention. These examples are indicative ofbut a few of the various ways in which the principles of the inventionmay be employed. Other ways in which the principles of the invention maybe employed and other objects, advantages and novel features of theinvention will be apparent from the detailed description of theinvention when consider in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a cross-sectional view schematic illustration of a testcontact system according to one aspect of the present invention.

FIG. 1b is a cross-section al vie w schematic illustration of the testcontact system of FIG. 1a taken along the line 1B.

FIG. 2 is a high level schematic illustration of a test contact systemaccording to another aspect of the present invention.

FIG. 3 is a high level schematic illustration of a test contact systemaccording to a further aspect of the present invention.

FIG. 4 is a high level schematic illustration of a test contact systemaccording to a further aspect of the present invention.

FIG. 5 is a flow diagram of a process according to a further aspect ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1a and 1 b schematically illustrate a test contact system 100exemplifying several aspects of the present invention. Test contactsystem 100 is part of a device handler that is part of an integratedcircuit device testing system. Test contact system 100 includes body110, tension adjustment screws 120, tension springs 122, primary contactplate 130, resilient members 140, secondary contact plate 150, andvacuum seals 160.

In operation of the integrated circuit device testing system, vacuumseals 160 of test contact system 100 are placed in contact with deviceunder test 180 and a vacuum is applied to hold device under test 180 totest contact system 100, which then carries device under test 180 to atest socket of a device tester. When test contact system 100 is inposition over the socket, the device handler exerts a contacting forcesufficient to establish reliable electrical contact between device undertest 180 and the test socket. Part of the contacting force is exertedthrough body 110 against the die of device under test 180. This force,which is generally from about 10 ft-lb/in² to about 30 ft-lb/in², issufficient to establish good thermal contact between the die and body110 without risking damage to the device under test. The balance of thecontacting force is exerted against the substrate of the device undertest through secondary contact plate 150.

The setting of tension adjustment screws 120 determines the distributionof the force between the die and the substrate. Tension adjustmentscrews 120 adjust the tension on springs 120. The portion of thecontacting force that is not exerted against the die is exerted throughsprings 122 against primary contact plate 130. The force from primarycontact plate 130 is transmitted through resilient members 140, whichprovide a cushioning effect. The force from resilient members 140 istransmitted to secondary contact plate 150 and from secondary contactplate 150 against the substrate of device under test 180.

After testing, test contact system 100 carries the device under testaway from the socket and the vacuum is released, whereupon the deviceunder test separates from vacuum seals 160. Vacuum seals 160 areconstructed using a foam-type material, which facilitates the release ofdevice under test 180.

Test contact system 100 has several novel features described more fullybelow. These features include a contact plate adapted to apply acontacting force against the substrate of the device under test, a forcedistribution system for adjustably distributing the total contactingforce between the substrate and a die of the device under test, anelastic member to cushion the force applied against the substrate, andvacuum seals with foam-type material construction.

The contacting force is exerted by the device handler through body 110of test contact system 100. Body 110 can be constructed of metal,re-enforced plastic, or any other suitable material. Body 110 generallyprovides a manifold for the vacuum exerted through vacuum seals 160.Body 110 can also provides for controlling the temperature of the deviceunder test, for example, with ducts for directing heated air to the testsite. Temperature stability can also be advanced by body 110 providing alarge thermal mass in proximity to the device under test to dissipateheat generated during testing. For this purpose, body 110 can beconfigured to contact the die of the device under test while secondarycontact plate 150 acts against the substrate of the device under test.Optionally, body 110 can be provided with a second contacting member forcontacting the die of the device under test. A contacting force can thusbe exerted on the die of the device under test while a contacting forceis also being exerted against the substrate of the device under test.

The total contacting force exerted against body 110, and through body110 to hold a device under test against a test socket, is fixed by thedevice handler in an amount determined by the testing system. But whenpart of the contacting force is exerted against the die, thedistribution of the contacting force between the substrate and the diecan be varied according to the settings of tension screws 120.

Tension adjustment screws 120 are supported by body 110 and act againsttension springs 122. This tension adjustment system is a specificexample of a broader concept, illustrated in FIG. 2. FIG. 2 is a highlevel schematic illustration of test contact system 200 that provides asystem for distributing the force from force generating system 210between die 240 and substrate 250 of the device under test. Test contactsystem 200 includes force distributing system 220 and force distributionadjustment system 230.

Force generating system 210 is a portion of the device handler,generally comprising a plunger, that generates a contacting force. Thetotal contacting force, which is generally determined by therequirements of a device contactor, is exerted by force generatingsystem 210.

Force distributing system 220 includes a mechanism for exerting a forceselectively against either die 240 or substrate 250 of the device undertest. This selectively exerted force is less than or equal to the forceexerted by force generating system 210. Where the selectively exertedforce is less, the balance of the force is passively applied against aportion of the device under test other than that to which theselectively exerted force is applied.

In one aspect of the invention, the selectively exerted force is exertedagainst die 240. In another aspect of the invention, the force isexerted against substrate 250. Suitable mechanism for exerting thisforce include, for example, springs, hydraulics, or piezoelectricelements. Force adjustment system 230 is designed with reference to themechanism used by force distribution system 220 to exert the force andcan include, for example, screws acting against springs, a pump andpressure regulator for hydraulics, or a voltage regulator forpiezoelectric elements.

The force distribution can be adjusted periodically to ensure the forceon the die remains at a level sufficient to establish satisfactorythermal contact between the die of the device under test and the forcedistributing system, which acts as a heat sink for the die. The force onthe die is generally from about 10 ft-lb/in² to about 30 ft-lb/in².

In test contact system 100, a force against the substrate is exertedthrough resilient member 140. Primary contacting plate 130 is providedto facilitate transfer of the contacting force from tension springs 122to resilient member 140. Springs 122 act against primary contactingplate 130. Resilient member 140, which is set within contacting plate130, extends to one side of contacting plate 130 and transfers the forceto secondary contacting plate 150.

Primary contacting plate 130, resilient member 140, and secondarycontacting plate 150 are a specific example of a broader concept,illustrated in FIG. 3. FIG. 3 is a high level schematic illustration oftest contact system 300. Test contact system 300 includes body 320 andresilient member 330. The force from force generating system 310 istransferred through body 320 and resilient member 330 to device undertest 350, whereby the force is cushioned. The construction of resilientmember 330 includes a material that serves to cushion the contactingforce as it is being applied to the device under test. For example,resilient member 140 can include, for example, fluorocarbon rubber,silicone, a butadiene/acrylonitrile copolymer, or another materialcommonly employed to make O-rings. In fact, a suitable elastic membercan be constructed from O-rings.

In test contact system 100, the force from resilient member 140 isexerted through secondary contacting plate 150, which applies the forceagainst the substrate of a device under test. Applying the contactingforce against the substrate of the device under test is another broadconcept, which is illustrated in FIG. 4. FIG. 4 is a high levelschematic illustration of test contact system 400. Test contact system400 includes body 420 and contacting plate 430. A contacting force fromforce generating system 410 is transferred through body 420 and contactplate 430. Contacting plate 430 is configured to transmit the contactingforce against substrate 454 of device under test 450.

Contacting plate 430 is configured with reference to device under test450, which includes substrate 452 and die 454. Generally, die 454 is atthe center of device under test 450 and contacting plate 430 isconfigured to contact the device under test along its periphery. Thus,contacting plate 430 can, for example, have a shape that is generallythat of a hollow rectangle or circle.

While the device under test can be any integrated circuit chip, whetherwire bonded to a lead frame or flip-chip mounted on a substrate, theinvention is particularly well suited for use with flip-chip mounteddies. In the flip-chip configuration, the die is usually not encased ina thermoset plastic, as is often the case with dies wire-bonded to leadframes. The flip-chips are often very small, about 1 cm wide or less,for example. The small size and exposed die make these flip-chips morefragile in comparison to device packages that are encapsulated inthermoset plastic. The invention in its several aspects providesdelicate handling of the devices.

Part of the handling operation is to pick up the devices and move them.Test contact system 100 provides a vacuum, applied through vacuum seals160 for this purpose. Vacuum seals 160 are constructed using a foam-typematerial, such as, for example a polyethylene, polyurethane, or epoxyfoam. The material is selected to be one that is less prone thansilicone to becoming sticky during high temperature testing.Non-sticking vacuum seals reduce the number of handler jams that resultfrom devices under test failing to disengage from the test contactsystem when suction is discontinued.

FIG. 5 is a flow diagram of a process 500 provided by a further aspectof the present invention. The contacting force and force distributionare initially set in step 510. The contacting force is generallyselected to provide a force close to the minimum sufficient to establishgood electrical communication between the devices under test and thetest socket. The force distribution is adjusted to provide a forceagainst the dies of the devices that is near the minimum of thatrequired to establish good thermal contact between the dies and the testcontact system.

In step 520, the test contact system is placed over a device to betested such that vacuum seals on the test contact system make contactwith the upper surface of the device. Typically, at this stage thedevice is in the input shuttle of an automated device handler of whichthe test contact system is one component. A vacuum is applied in step530, whereby the device is held to the test contact system and can becarried over to the test socket. In step 540, the test contact systemplaces the device into the test socket. After the device has been testedin step 550, the device is taken to an output shuttle in step 560. Therecan be a plurality of output shuttles and the output shuttle selectedcan depend on the test results, whereby the devices are sorted. At theoutput shuttle, in step 570, the vacuum is released and the deviceseparates from the test contact system.

At this point, in step 580, a decision can be made. Either the testcontact system returns immediately to pick up another device for testingor the contacting force and/or force distribution are adjusted. The needto adjust the contacting force can be determined in several ways. Forexample, a need to adjust the contacting force can be determined by testresults that are indicative of inadequate contacting between the deviceunder test and the test socket. In another example, an operator, orautomatic inspection system, can signal the need to adjust thecontacting force distribution based on an observation that a deviceunder test has been damaged during testing. The decision can be madeautomatically, by a controller, or by an operator.

What has been described above is the present invention and several ofits specific aspects. It is, of course, not possible to describe everyconceivable combination of components or methodologies for purposes ofdescribing the present invention, but one of ordinary skill in the artwill recognize that many further combinations and permutations of thepresent invention are possible. Accordingly, the present invention isintended to embrace all such alterations, modifications and variationsthat fall within the spirit and scope of the appended claims.Furthermore, where the term “includes” has been used it is intended tobe inclusive in a manner similar to the term “comprising.”

What is claimed is:
 1. A test contact system for exerting a contactingforce against an integrated circuit device that comprises an un-encaseddie attached to a substrate, comprising: a body; and a contact platesupported by the body; wherein the contact plate exerts at least asubstantial portion of the contacting force against the substrate of theintegrated circuit device, and wherein a portion of the contacting forceis exerted against the die.
 2. The test contact system of claim 1,wherein all of the contacting force is exerted against the substrate. 3.The test contact system of claim 1, wherein the distribution of thecontacting force between the substrate and the die is adjustable.
 4. Thetest contact system of claim 3, wherein the portion of the contactingforce exerted against the substrate is exerted through springs and thedistribution of the contacting force is adjustable through set screwsacting against the springs.
 5. The test contact system of claim 3,wherein the contacting force exerted by the contact plate against thesubstrate is transmitted through a resilient member.
 6. The test contactsystem of claim 1, wherein the contacting force exerted by the contactplate against the substrate is transmitted through a resilient member.7. A test contact system, comprising: a body; and a vacuum seal attachedto the body for picking up, holding, and moving a device under test tothe body; wherein the vacuum seal comprises a foam type material.
 8. Atest contact system, comprising: means for exerting a contacting forceagainst an integrated circuit device; wherein the integrated circuitdevice comprises an un-encased die attached to a substrate and at leasta substantial portion of the contacting force is exerted against thesubstrate of the integrated circuit device; and means for adjusting adistribution of the contacting force between the substrate and the die.9. A method of testing an integrated circuit device, comprising: whiletesting the integrated circuit device, exerting a contacting force tohold the integrated circuit device in contact with a socket of a devicetester; wherein at least a substantial portion of the contacting forceis exerted against a substrate of the integrated circuit device, andwherein a distribution of the contacting force between the substrate ofthe integrated circuit device and a die of the integrated circuit deviceis adjustable.
 10. The method of claim 9, the portion of the contactingforce exerted against the substrate is exerted through a resilientmember.
 11. The method of claim 9, wherein the integrated circuit deviceis a flip chip comprising an un-encased die.
 12. The method of claim 9,further comprising carrying the integrated circuit device to the socketwhile holding the integrated circuit device to a handler using a vacuumand a vacuum seal.
 13. The method of claim 12, wherein the vacuum sealcomprises a foam type material.
 14. The method of claim 9, wherein theforce is exerted by a test contact system that also serves to dissipateheat from the integrated circuit device during testing.
 15. The methodof claim 14, wherein the test contact system contacts the die of theintegrated circuit device.